The present invention relates generally to light beam polarization devices and more particularly to a light beam polarization converter for electro-optical devices, such as a liquid crystal projection displays.
With the advent of the information technology (IT) age, there is an increasing demand for various electro-optical displays, such as liquid crystal projection type television displays. In this type of display, the light source is not inherently integrated, and thus an external source may be required for image display. As the demand for higher quality displays increases, it is becoming more and more important that the utilization efficiency of light sources should be enhanced. A conventional way to increase efficiency is to convert the non-polarized light beams of a light source into linearly polarized light beams having a single polarization state, as disclosed in, for example U.S. Pat. No. 5,122,895 (Polarization converter for converting randomly polarized light to linearly polarized light to Takanashi et al.). Wherein a conventional converter, the so-called P-S converter is disclosed. The P-polarized light component refers to the optical component of the electric field oscillation direction that is parallel to the plane of the incident light beam. The S-polarized light component is the optical component perpendicular to that plane.
As shown in prior art FIG. 1, in a conventional liquid crystal projection type television, the light beam emitted from a light source 10 is projected through a projection lens onto a display (not shown) through the processing of a parallelizing lens 11, a diverging plate 12, a P-S converter 13, splitter lenses 14 and 15, a reflecting mirror 16 and respective liquid crystal displays 301, 302 and 303. The main function of the P-S converter 13 is to reduce the optical loss of light beams when screened through the liquid crystal displays 301, 302 and 303 for specific polarization.
FIG. 2 shows a schematic perspective view of a conventional P-S converter 70. The non-polarized light beams I emitted from a light source travels from the bottom side of P-S converter 70, is converted therein and emitted from the top side as a single S-polarized state light beam.
FIG. 3 shows a typical optical path of a light beam in a conventional P-S converter. The description is illustrated utilizing one (designated xe2x80x9cI1xe2x80x9d) of a plurality of light beams emanating from the light source. The light beam I1 is incident to the P-S converter through an anti-reflection film 70, and then subsequently becomes a light beam I2 having both P- and S-polarization states. The light beam I2 is then incident on a polarization state splitter film 73 with a P-component I4 penetrating through the splitter film 73 and being converted by a half wave plate 78. Light beam I4 then travels further through an anti-reflection film 79 and becomes a light beam 16 of S-polarization state. The component of the light beam I2 failing to penetrate through the splitter film 73 is reflected and becomes a light beam I3 of S-polarization state, after which the light beam I3 is reflected by a highly reflective film 75 and penetrates through an anti-reflection film 77. Finally, the output thereof is a light beam 16 of S-polarization state. Since the above effect of polarization conversion may not be obtained if the light beam emitted from the light source is incident to the portion 81 as shown in FIG. 3, the conventional P-S converter may only achieve efficiencies of at best 50% in converting the polarization state of light beams. In addition to such lack of efficiency, the configuration of conventional P-S converters is complex and typically involves relatively high costs of production. It is also known in the art that a conventional display incorporating such a conventional converter is notorious for high power consumption.
In view of the above problems, the first object of the present invention is to provide a light beam polarization converter for converting an illumination source into a single polarization light source, which may convert the light at extremely low optical loss and is suitable for mass production in terms of production cost.
The second object of the present invention is to provide a light beam polarization converter for converting an illumination source into a single polarization light source, which is easy to use or to add on to a conventional apparatus.
To achieve the first object, the present invention provides a light beam polarization converter for converting an illumination light source into a polarization light source, comprising an under plate having an undulated lower surface and a ridged upper surface; a substrate having a ridged lower surface, substantially complementary to the upper surface of the under plate and facing therewith, and a ridged upper surface; a phase retardation film of high reflectivity disposed partially between the substrate and the under plate; a top cover having a lower surface, substantially complementary to the upper surface of the substrate and facing therewith, and an upper surface; and a polarization splitter film disposed between the substrate and the top cover.
For achieving enhanced optical performance, the ridge pitch of the ridged surfaces may be constant or varied, and the ridge lines thereof are arranged as being not parallel to each other, thus allowing greater freedom of converter design. Moreover, the lower surface of the under plate and the upper surface of the top cover may respectively have various undulations, such as cylindrical, spherical or non-spherical, corresponding to each other in a conjugate way to control the optical output angle, and thus enhance the transmitting efficiency of light beams while passing through the converter.
To achieve the second object, the present invention provides a light beam polarization converter for converting an illumination light source into a polarization light source, comprising an under plate having an undulated lower surface and a ridged upper surface; a substrate having a ridged lower surface, substantially complementary to the upper surface of the under plate and facing therewith, and a substantially flat upper surface; a phase retardation film of high reflectivity provided partially between the substrate and the under plate; a top cover film having a flat lower surface, substantially complementary to the upper surface of the substrate and facing therewith, and a ridged upper surface; a top cover having a lower surface, substantially complementary to the upper surface of the top cover film and facing therewith, and an upper surface; and a polarization splitter film provided between the upper surface of the top cover film and the lower surface of the top cover.
With the above top cover film, which is soft and flexible when joined with the top cover and the polarization splitter film, it is very convenient to apply this soft configuration onto the under plate and achieve the effect and advantage in accordance with the present invention.
With the configuration disclosed in accordance with the present invention, the light beam polarization converter is simple and easy to produce, and achieves optical efficiency no less than that of a conventional one. In particular, the present invention provides a significant advantage of quick adaptation to conventional optical devices.